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jeremybenn |
/*******************************************************************************
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*
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* Copyright (c) 1993 Intel Corporation
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*
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* Intel hereby grants you permission to copy, modify, and distribute this
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* software and its documentation. Intel grants this permission provided
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* that the above copyright notice appears in all copies and that both the
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* copyright notice and this permission notice appear in supporting
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* documentation. In addition, Intel grants this permission provided that
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* you prominently mark as "not part of the original" any modifications
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* made to this software or documentation, and that the name of Intel
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* Corporation not be used in advertising or publicity pertaining to
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* distribution of the software or the documentation without specific,
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* written prior permission.
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*
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* Intel Corporation provides this AS IS, WITHOUT ANY WARRANTY, EXPRESS OR
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* IMPLIED, INCLUDING, WITHOUT LIMITATION, ANY WARRANTY OF MERCHANTABILITY
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* OR FITNESS FOR A PARTICULAR PURPOSE. Intel makes no guarantee or
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* representations regarding the use of, or the results of the use of,
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* the software and documentation in terms of correctness, accuracy,
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* reliability, currentness, or otherwise; and you rely on the software,
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* documentation and results solely at your own risk.
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*
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* IN NO EVENT SHALL INTEL BE LIABLE FOR ANY LOSS OF USE, LOSS OF BUSINESS,
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* LOSS OF PROFITS, INDIRECT, INCIDENTAL, SPECIAL OR CONSEQUENTIAL DAMAGES
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* OF ANY KIND. IN NO EVENT SHALL INTEL'S TOTAL LIABILITY EXCEED THE SUM
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* PAID TO INTEL FOR THE PRODUCT LICENSED HEREUNDER.
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*
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******************************************************************************/
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.file "strncat.s"
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#ifdef __PIC
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.pic
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#endif
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#ifdef __PID
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.pid
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#endif
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/*
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* (c) copyright 1988,1993 Intel Corp., all rights reserved
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*/
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/*
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procedure strncat (optimized assembler version for the 80960K Series)
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dest_addr = strncat (dest_addr, src_addr, max_bytes)
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append the null terminated string pointed to by src_addr to the null
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terminated string pointed to by dest_addr. Return the original
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dest_addr. If the source string is longer than max_bytes, then
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append only max_bytes bytes, and tack on a null byte on the end.
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This routine will fail if the source and destination string
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overlap (in particular, if the end of the source is overlapped
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by the beginning of the destination). The behavior is undefined.
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This is acceptable according to the draft C standard.
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Undefined behavior will also occur if the end of the source string
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(i.e. the terminating null byte) is in the last two words of the
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program's allocated memory space. This is so because strncat fetches
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ahead. Disallowing the fetch ahead would impose a severe performance
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penalty.
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Strategy:
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First, skip to the null byte in the destination string. Then
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fetch the source string by words and store them by words to the
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destination string, until there are fewer than three bytes left
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to copy. Then, using the last word of the source (the one that
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contains the remaining 0, 1, 2, or 3 bytes to be copied), store
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a byte at a time until Ldone.
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If, before exhausting the max_byte count, the null byte is encountered
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in the source string, then just copy up thru the null byte.
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Tactics:
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1) Do NOT try to fetch and store the words in a word aligned manner
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because, in my judgement, the performance degradation experienced due
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to non-aligned accesses does NOT outweigh the time and complexity added
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by the preamble and convoluted body that would be necessary to assure
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alignment.
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*/
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.globl _strncat
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.globl __strncat
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.leafproc _strncat,__strncat
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.align 2
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_strncat:
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#ifndef __PIC
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lda Lrett,g14
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#else
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lda Lrett-(.+8)(ip),g14
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#endif
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__strncat:
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mov g14,g6
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cmpibge 0, g2, Lno_operation # Lexit early if max_bytes <= 0
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mov g0, g5
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Lskip_word_loop:
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ld (g5), g7 # fetch word of dest string
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addo 4, g5, g5 # post-increment dest ptr
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scanbyte 0, g7 # does it contain null byte?
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bno Lskip_word_loop # if not, loop
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subo 5, g5, g5 # adjust dest ptr
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lda 0xff, g3 # byte extraction mask = 0xff;
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Lskip_byte_loop:
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and g7, g3, g14 # extract byte of last word of dest string
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cmpo 0, g14 # is it null?
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addo 1, g5, g5 # adjust dest ptr
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shro 8, g7, g7 # position next byte for extraction
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bne Lskip_byte_loop # loop if null not found yet
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ld (g1), g7 # fetch first word of source string
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Lwloop: # word copying loop
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cmpo 4, g2 # max_bytes < 4 ?
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addo 4, g1, g1 # post-increment source ptr
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bge Lcloop.a # branch if less than 4 bytes to move
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scanbyte 0, g7 # is null byte reached yet?
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mov g7, g4 # keep a copy of the source word
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be Lcloop # branch if null byte reached
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ld (g1), g7 # pre-fetch next word of source
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subo 4, g2, g2 # reduce max_byte counter
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st g4, (g5) # store current word
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addo 4, g5, g5 # post-increment destination ptr
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b Lwloop
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Lcloop.b:
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addo 1, g5, g5 # post-increment destination ptr
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shro 8, g7, g7 # position next byte for extraction
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Lcloop: # character copying loop (max_byte > 3)
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and g3, g7, g4 # extract character
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cmpo 0, g4 # is it null?
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stob g4, (g5) # store it
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bne Lcloop.b # loop if null not encountered yet
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bx (g6) # g0 = dest string address; g14 = 0
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Lrett:
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ret
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Lcloop.c:
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addo 1, g5, g5 # post-increment destination ptr
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shro 8, g7, g7 # position next byte for extraction
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Lcloop.a: # character copying loop (max_byte <= 3)
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cmpdeco 0,g2,g2 # max_byte == 0?
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and g3, g7, g4 # extract character
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be Ldone # store null and Lexit if max_byte exhausted
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cmpo 0, g4 # is it null?
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stob g4, (g5) # store it
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bne Lcloop.c # loop if null not encountered yet
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Ldone: stob g14, (g5) # store trailing null
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bx (g6) # g0 = dest string address; g14 = 0
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Lno_operation: mov 0, g14 # conform to register conventions
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bx (g6)
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/* end of strncat */
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